Is London England far south enough to get a truly dark sky - without astronomical twilight on the northern horizon at night in middle of June?

London's latitude is approximately 51.5 degrees north. During the middle of June, the Sun reaches a maximum altitude of about 57 degrees above the northern horizon at noon. So, strictly speaking, astronomical twilight will last through the entire night in London during this time.

On the other hand, the duration of astronomical twilight decreases toward the middle of the night, and the sky can become reasonably dark if you travel a short distance north or south out of the city. For example, if you travel about 100 kilometers north of London, the Sun will reach a maximum altitude of only about 47 degrees above the northern horizon, which is low enough that astronomical twilight will end around 11 pm or midnight.

Also, it is important to consider the amount of light pollution from nearby cities and towns, as well as the weather conditions. Light pollution can make it more difficult to see faint stars and galaxies, even if the sky is otherwise dark. Additionally, if the sky is cloudy, then the darkness of the sky will be limited.

Overall, while it is possible to find dark skies in the vicinity of London, it is not far enough south to experience truly dark skies in middle of June without any astronomical twilight.